This invention relates to an optical access system, and more particularly, to a technology of controlling optical communication path switching in an optical access system that uses an optical switch to switch optical communication paths.
An optical access system with a passive optical network (PON) has become popular as a way to access the Internet at high speed. Variations of PON technology include an Ethernet passive optical network (EPON) defined in IEEE Std 802. 3TM-2005 and a Gigabit-capable passive optical network (GPON) defined in ITU-T Recommendation G. 984.1.
A PON includes an optical line terminal (OLT), which terminates an optical fiber on the side of a central office of a telecommunications carrier, an optical network unit (ONU), which terminates an optical fiber on the user terminal side, and a splitter, which splits an optical fiber led out of the OLT up among a plurality of the ONUs.
Being a passive device, the splitter keeps the cost of building the network low. The splitter, however, splits a signal into as many copies as the total count of ONUs, allowing the signal to reach other ONUs in addition to the originally intended receiver of the communication. The resultant problem is that satisfactory secrecy is not always guaranteed. Further, signal branching in the splitter lowers the optical signal power and presents a problem that an increase in number of branches shortens the communicable distance.
As a solution to those problems of PONs, there has been proposed a network in which an optical switch, which is an active device, is used to split an optical fiber in place of the splitter provided in a PON (see, for example, JP 2006-246262 A, JP 2007-67948 A, IEICE TRANS. COMMUN., VOL. E89-B, NO. 3 pp. 724-730, and IEICE TRANS. COMMUN., VOL. E89-B, NO. 11 pp. 3021-3031).